International patent application WO-2006/037822-A1, belonging to the current applicant, discloses a device for steering a self-orienting wheel of a human-driven vehicle, where the  self-orienting wheel to be guided is one of the wheels on which the vehicle moves in normal conditions. The operation of the device is based on providing a steering mechanism and a clutch mechanism which can optionally be operated to couple said steering mechanism to a rotating support on which the self-orienting wheel is mounted. The mentioned steering and clutch mechanisms are distributed in a control unit fixed, for example, to a push bar located in a rear end region of the vehicle, and a steering unit associated with the self-orienting wheel to be driven, which is located, for example, in a front end region of the vehicle. The partial mechanisms housed in the control and steering units are mutually connected by respective movement transmission devices, such as, for example, Bowden type flexible cable and sheath assemblies. Elastic means push the clutch mechanism towards an uncoupled position and the mentioned control unit includes a command member at the disposal of the user to remotely operate the clutch mechanism against the force of said elastic means and the steering mechanism.
The device of the mentioned international patent application WO-2006/037822-A1 is fully operative, although it has some aspects which can be improved. For example, the implementation of the clutch mechanism requires an adaptation to the self-orienting wheel to be driven and, due to the fact that there is a large variety of self-orienting wheel models, a specific design of part of the clutch mechanism is required for each model if the device is to be applied to a variety of pre-existing vehicles. Furthermore, the coupling of the clutch mechanism is only performed when the self-orienting wheel is in a predetermined angular position in relation to a coupling part of the clutch mechanism, which forces the user to perform a certain maneuver with the vehicle in addition to manually acting on the command member to carry out the coupling.
Document EP-1238885-A1 discloses a carriage provided with self-orienting wheels, which includes an additional steerable and power-driven wheel at an end of the carriage. The mentioned orientable wheel is mounted on a supported connected to a mechanism operated by means of a handle which allows lowering the support until putting the orientable wheel in contact with the ground, and raising the support to put the orientable wheel out of contact with the ground. The raising and lowering mechanism comprises a tubular column fixed to the chassis of the carriage and a slide bar inserted in said tubular column, where the support of the wheel is fixed to the lower end of the slide bar and the handle is installed at the upper end of the tubular column to rotate with respect to a horizontal axis and connected to the upper end of the slide bar by means of an eccentric mechanism. The handle can thus be shifted between a horizontal position and a vertical position to raise or lower the orientable wheel and can be rotated with respect to a vertical axis to vary the orientation of the orientable wheel. A locking mechanism allows locking the handle in the horizontal position.
A drawback of the carriage described in the mentioned document EP-1238885-A1 is that the control handle is located at the same end of the carriage where the orientable wheel is located, which is unsuitable for a human-driven vehicle, such as a shopping cart, where the most suitable situation for a steering wheel is the front end region of the vehicle while the vehicle is generally pushed by the user by means of a push bar or another resistant structure located in the rear end region of the vehicle.